They are actually symbols that can represent sentences in few line, but at times i find it very difficult to locate the right emoji since they are voluminous.
Facebook will be boring without emojis, but sometimes a conversation may seem boring if the whole display is purely emoji, oh how will I feel when a dm hi and you drop 👋, if I move ahead to drop, how are you?, then I see 💃💃💃, it will be obvious you don't want to continue the conversation, so backing off will be the best option, what I am saying in essence is that emoji can only support language, shorten it quicken conversations but cannot stand independently as a language.